Heretofore, heavy duty tires such as a tire for truck and bus, a tire for construction vehicle and the like have been used under a very high load, so that it is generally and widely attempted to prevent settling of a bead portion, rim chafing and rim slippage and the like and to improve an air sealing property and the like by disposing a rubber chafer in at least a part of the bead portion contacting with a rim. In the tire provided with the rubber chafer, an innerliner is arranged in the inner face of the tire for the purpose of improving the air sealing property of the tire, in which an end of the innerliner is usually located in the vicinity of a toe end of the bead portion and a part of the innerliner overlaps partially with the rubber chafer. In this tire, however, the adhesiveness between the innerliner and the rubber chafer is poor, so that there is a problem that when a joint portion between the innerliner and the rubber chafer is particularly located in the vicinity of the toe end, cracks easily occur at an interface between the innerliner and the rubber chafer during the running on the market.
Moreover, when the innerliner is comprised of plural layers and a end of an outermost layer in the innerliner extends to the part contacting with the rim over the toe end, the outermost layer of the innerliner may ride up due to the rubbing or the like by contacting with the rim. To the contrary, when the end of the outermost layer in the innerliner is arranged so as not to arrive at the toe end, there is a problem that a rubber member of the bead portion is deteriorated by oxygen penetrated from the toe end.
On the other hand, there is proposed a tire in which the penetration of the oxygen from the toe end part is suppressed by using in the rubber chafer a rubber composition comprising 20-60 parts by weight in total of butyl rubber and/or halogenated butyl rubber and 80-40 parts by weight in total of cis-1,4-polyisoprene rubber and epoxidized cis-1,4-polyisoprene rubber as a rubber component (see JP-A-7-90125). In this case, however, there is a problem that the rubber chafer cannot play its original role sufficiently because a ratio of the butyl rubber and the halogenated butyl rubber in the rubber composition for the rubber chafer is higher than that in the conventional technique.
As the tire provided at its bead portion with the rubber chafer, there is proposed a tire in which a rubber layer having a high air impermeability is arranged on the toe end part of the bead portion to suppress the penetration of oxygen from the toe end part (see JP-A-H07-502471). In this case, however, it is necessary to use a rubber composition having a high ratio of a rubber component having a high air impermeability such as butyl rubber, halogenated butyl rubber or the like in the rubber layer for sufficiently increasing the air impermeability of the rubber layer arranged at the toe end part, so that it is difficult to assure the adhesiveness between the rubber layer and the rubber chafer.
As the tire provided at its bead portion with the rubber chafer, there is further proposed a tire in which an innerliner is arranged so as to entangle the bead core to improve the air-retaining property of the tire (see JP-A-2001-233013). Even in this case, however, the adhesiveness between the innerliner and the rubber chafer is still low, so that it is impossible to overcome a problem that cracks are easily generated at the interface between the innerliner and the rubber chafer during the running on the market.